Surface Plasmon Resonance (SPR) is a well-known optical diagnostics method used extensively by biologists to sensitively measure changes at surfaces. For insight it is noted that normally electromagnetic radiation reflects speculatly from smooth surfaces, or diffusely from rough surfaces, or reflects with combined specular and diffuse components. Surface Plasmon Resonance (SPR) refers to an unusual condition under which the light, rather than being immediately reflected, is absorbed and induces a surface “plasmon” or the like wave in the material. This occurs when using, for example, a gold film, and P-Polarized visible light (of say 650 nm wavelength) is caused to impinge upon thereupon at an SPR resonance angle of incidence of about 50 degrees to the normal to a surface thereof. This is described as a “resonant” condition for SPR. The P-Polarized light, (eg. which can comprise electromagnetic radiation of any functional wavelength), sets up a surface plasmon traveling wave along the surface of a metal. To date, SPR invariably uses either gold, silver, or other common metal for which plasmons are excited mainly by visible light. That is, the atomic nature of the material (metal) determines the resonant angle. In scientific terms, SPR can be performed on any material for which the real-part of the complex dielectric function (e1) is less than zero, in a wavelength region wherein imaginary part (e2) of the is complex dielectric function is not too great. Materials with negative real-part of dielectric function is useful wavelength ranges include especially low-mass materials, such as SiC, and Si-oxides. For example, SiC with real-part of dielectric constant. negative in spectral range 960 cm−1 to 780 cm−1, and AIN has range 610 cm−I to 800 cm−1 negative dielectric function. SiO2 (quartz) is 1161 cm−1 to 1236 cm−1. Hexagonal BN has useful ranges 1510 cm−1 to 1595 cm−1 and 1367 cm−1 to 1610 cm−1, and cubic BN in range 1060 cm−1 to 1430 cm−1. Graphite has possible resonance 867.8 cm−1 to 868.1 cm−1; narrow but potentially useful. Heavily doped binary, ternary, and quaternary alloys of compound 3/I semiconductors move the resonance into the useful 2 to 18 micron spectral range (555 cm−1 to 5000 cm−1) for biological materials (see attached review article table and graphs). Other examples might be intercalation compounds of graphite, which dope as both donors and acceptors. Metals have negative real-part of dielectric function negative at long-wavelengths, but are difficult to excite, but are possibly useful for these measurements, especially ultra-smooth metals such as Ir.
Continuing, SPR can, sense both the time rate of change and the amount of attachment of biomaterial to a metal substrate. SPR is a known valuable method for development of new drug-release surfaces; development of sensors for toxins, bio-warfare threats, and diseases, development of new materials for implants in humans (such as stints and heart valves), and for numerous other biomedical and bioengineering applications. SPR is hundreds of times more sensitive than conventional spectroscopies for thin films. One example, (of hundreds), is in the monitoring of the attachment of toxins, (such as cholera), to surfaces functionallized by IgG protein. To date most applications have been in bio-material monitoring.
While the herein disclosed invention can be used in any material system investigation system such as Polarimeter, Reflectomerter, Spectrophotometer and the like Systems, an important application is with Ellipsometer Systems, whether monochromatic or spectroscopic. It should therefore be understood that Ellipsometry involves acquisition of sample system characterizing data at single or multiple Wavelengths, and at one or more Angle(s)-of-Incidence (AOI) of a Beam of Electromagnetic Radiation to a surface of the sample system. Ellipsometry is generally well described in a great many publication, one such publication being a review paper by Collins, titled “Automatic Rotating Element Ellipsometers: Calibration, Operation and Real-Time Applications”, Rev. Sci. Instrum., 61(8) (1990).
A typical goal in ellipsometry is to obtain, for each wavelength in, and angle of incidence of said beam of electromagnetic radiation caused to interact with a sample system, sample system characterizing PSI and DELTA values, where PSI is related to a change in a ratio of magnitudes of orthogonal components rp/rs in said beam of electromagnetic radiation, and wherein DELTA is related to a phase shift entered between said orthogonal components rp and rs, caused by interaction with said sample system. This is expressed by:TAN(ψ) ei(Δ)=rs/rp.(Note the availability of the phase DELTA (Δ) data is a distinguishing factor between ellipsometry and reflectometry).
Ellipsometer Systems generally include a source of a beam of electromagnetic radiation, a Polarizer, which serves to impose a state of polarization on a beam of electromagnetic radiation, a Stage for supporting a sample system, and an Analyzer which serves to select a polarization state in a beam of electromagnetic radiation after it has interacted with a material system, and passed it to a Detector System for analysis therein. As well, one or more Compensator(s) can be present and serve to affect a phase angle between orthogonal components of a polarized beam of electromagnetic radiation. A number of types of ellipsometer systems exist, such as those which include rotating elements and those which include modulation elements. Those including rotating elements include Rotating Polarizer (RP), Rotating Analyzer (RA) and Rotating Compensator (RC). A preferred embodiment is a Rotating Compensator Ellipsometer System because, it is noted, Rotating Compensator Ellipsometer Systems do not demonstrate “Dead-Spots” where obtaining data is difficult. They can read PSI and DELTA of a Material System over a full Range of Degrees with the only limitation being that if PSI becomes essentially zero (0.0), DELTA can not then be determined as there is not sufficient PSI Polar Vector Length to form the angle between the PSI Vector and an “X” axis. In comparison, Rotating Analyzer and Rotating Plarizer Ellipsometers have “Dead Spots” at DELTA's near 0.0 or 180 Degrees and Modulation Element Ellipsometers also have “Dead Spots” at PSI near 45 Degrees). The utility of Rotating Compensator Ellipsometer Systems should then be apparent. Another benefit provided by fixed Polarizer (P) and Analyzer (A) positions is that polarization state sensitivity to input and output optics during data acquisition is essentially non-existent. This enables relatively easy use of optic fibers, mirrors, lenses etc. for input/output.
Further, it is to be understood that causing a polarized beam of electromagnetic radiation to interact with a sample system generally causes change in the ratio of the intensities of orthogonal components thereof and/or the phase angle between said orthogonal components. The same is generally true for interaction between any system component and a polarized beam of electromagnetic radiation. In recognition of the need to isolate the effects of an investigated sample system from those caused by interaction between a beam of electromagnetic radiation and system components other than said sample system, (to enable accurate characterization of a sample system per se.), this Specification incorporates by reference the regression procedure of U.S. Pat. No. 5,872,630 to Johs et al. in that it describes simultaneous evaluation of sample characterizing parameters such as PSI and DELTA, as well system characterizing parameters, and this Specification also incorporates by reference the Vacuum Chamber Window Correction methodology of U.S. Pat. No. 6,034,777 to Johs et al. to account for phase shifts entered between orthogonal components of a beam of electromagnetic radiation, by disclosed invention system windows and/or beam entry elements. For insight, one embodiment of said method of accurately evaluating parameters in parameterized equations in a mathematical model of a system of spatially separated input and output windows, said parameterized equations enabling, when parameters therein are properly evaluated, independent calculation of retardation entered by each of said input window and said output window between orthogonal components of a beam of electromagnetic radiation caused to pass through said input and output windows, at least one of said input and output windows being birefringent, said method comprises, in a functional order, the steps of:                a. providing spatially separated input and output windows, at least one of said input and output windows demonstrating birefringence when a beam of electromagnetic radiation is caused to pass therethrough, there being a means for supporting a sample system positioned between said input and output windows;        b. positioning an ellipsometer system source of electromagnetic radiation and an ellipsometer system detector system such that in use a beam of electromagnetic radiation provided by said source of electromagnetic radiation is caused to pass through said input window, interact with said sample system in a plane of incidence thereto, and exit through said output window and enter said detector system;        c. providing a sample system to said means for supporting a sample system, the composition of said sample system being sufficiently well known so that retardence entered thereby to a polarized beam of electromagnetic radiation of a given wavelength, which is caused to interact with said sample system in a plane of incidence thereto, can be accurately modeled mathematically by a parameterized equation which, when parameters therein are properly evaluated, allows calculation of retardence entered thereby between orthogonal components of a beam of electromagnetic radiation caused to interact therewith in a plane of incidence thereto, given wavelength;        d. providing a mathematical model for said ellipsometer system and said input and output windows and said sample system, comprising separate parameterized equations for independently calculating retardence entered between orthogonal components of a beam of electromagnetic radiation caused to pass through each of said input and output windows and interact with said sample system in a plane of incidence thereto; such that where parameters in said mathematical model are properly evaluated, retardence entered between orthogonal components of a beam of electromagnetic which passes through each of said input and output windows and interacts with said sample system in a plane of incidence thereto can be independently calculated from said parameterized equations, given wavelength;        e. obtaining a spectroscopic set of ellipsometric data with said parameterizable sample system present on the means for supporting a sample system, utilizing a beam of electromagnetic radiation provided by said source of electromagnetic radiation, said beam of electromagnetic radiation being caused to pass through said input window, interact with said parameterizable sample system in a plane of incidence thereto, and exit through said output window and enter said detector system;        f. by utilizing said mathematical model provided in step d. and said spectroscopic set of ellipsometric data obtained in step e., simultaneously evaluating parameters in said mathematical model parameterized equations for independently calculating retardence entered between orthogonal components in a beam of electromagnetic radiation caused to pass through said input window, interact with said sample system in a plane of incidence thereto, and exit through said output window;to the end that application of said parameterized equations for each of said input window, output window and sample system for which values of parameters therein have been determined in step f., enables independent calculation of retardence entered between orthogonal components of a beam of electromagnetic radiation by each of said input and output windows, and said sample system, at given wavelengths in said spectroscopic set of ellipsometric data, said calculated retardence values for each of said input window, output window and sample system being essentially uncorrelated.        
No known references teach combined use of Surface Plasmon Resonance data which is obtained using P-Polarized electromagnetic radiation directed to a substrate surface at a Resonance angle-of-incidence, and conventional ellipsometric data which is obtained using other than P-Polarized electromagentic radiation applied at said SPR Resonance angle-of-incidence, or electromagneic radiation of any Polarization applied at other than said Resonance angle-of-incidence, in monitoring and optionally controlling thin film deposition or removal from the surface of said substrate.